Stuttering is a disorder of speech with a prevalence estimated to be 1% of the World's population. It is often a significant handicap for the individual and can limit employment opportunities; and social and psychological adjustment. The etiology of stuttering is unknown, and standardized, successful treatments for stuttering have not been developed. A major impediment to understanding the etiology of stuttering and to the development of successful therapeutic techniques is the lack of understanding of the physiological bases of the disorder. Stuttering manifests itself as a breakdown in speech motor processes. The complex variables known to affect the occurrence of stuttering, such as emotional state or speaking situation, must ultimately have an effect on the physiological events necessary for the production of speech. Therefore, to understand stuttering it is essential to understand the physiological mechanism underlying the disruptions of speech motor behavior in stuttering. The research proposed in this application addresses two general questions: What are the physiological correlates of speech breakdown in stuttering and is stuttering a disorder that arises, in part, from a generalized deficit in sensorimotor organization? The specific aims are (1) to provide quantitative analyses of activity of articulatory, laryngeal, and respiratory muscles prior to, during, and after disfluencies, (2) to determine if changes in autonomic function are associated with stuttering, (3) to use electromyographic, kinematic, and autonomic measures to develop pattern recognition algorithms to determine if there is a consistent set of physiological events that is associated with disfluent behavior and that can be used to recognize impending breakdowns, and (4) to determine if stutterers can be discriminated from nonstutterers on the basis of measures of timing performance in a wide range of motor behaviors.